Weft inserting arrangement of fluid-jet loom

ABSTRACT

A weft inserting arrangement for use in a fluid-jet shuttleless loom using a solenoid-operated fluid flow control valve so that it is opened and closed in accordance with electric signals generated in synchronism with operating cycles of the loom and also so, that the timing and duration of the weft inserting cycles can be adjusted easily and precisely in accordance with the operating conditions of the loom and/or depending upon the types and counts of the weft yarns woven into cloth. The weft inserting arrangement may further have a fluid accumulator for projecting the weft yarn at a decreasing velocity so that the weft yarn in the shed of warp yarns is under a uniform tension.

22 Filed:

[ 1 WEFT HNSERTING ARRANGEMENT OF FLUllD-JET LOOM [75] Inventors: Miyoki Gotoh; Yukio Mizuno;

Kazno Shibata, all of Tokyo, Japan [73] Assignee: Nissan Motor Company, Limited,

Yokohama, Japan Feb. 7, 11973 21 Appl. No.: 330,309

[30] Foreign Application Priority Data Feb. 15, 1972 Japan 47-15915 Feb. 7, 1972 Japan.. 47-13484 [52] us. Cl. 139/1271? [51] lint. Cl D03d 47/30, B65h 17/32 [58] Field of Search 226/7, 97; 239/410, 411; 139/127 P [56] References Cited UNITED STATES PATENTS 3,519,030 7/1970 Vermeulen 139/12-7 3,672,406 6/1972 Vermeulen 139/ 1 27 Primary Examiner-Henry S. Jaudon Attorney, Agent, or Firm-Robert E. Burns; Emmanuel J. Lobato [57] ABSTRACT A weft inserting arrangement for use in a fluid-jet shuttleless loom using a solenoid-operated fluid flow control valve so that it is opened and closed in accordance with electric signals generated in synchronism with operating cycles of the loom and also so, that the I timing and duration of the weft inserting cycles can be adjusted easily and precisely in accordance with the operating conditions of the loom and/or depending upon the types and counts of the weft yarns woven into cloth. The weft inserting arrangement may further have a fluid accumulator for projecting the weft yarn at a decreasing velocity so that the weft yarn in the shed of warp yarns is under a uniform tension.

4 Claims, 7 Drawing Figures pmm gumm amm 3,828,829

SHEU 1 0f 3 NOZZLE FLUID .8 JET FLU l D SOURCE SIGNAL GEN. 7 8 50 l a 42 [PPE. PULSE AMP. MODIFIER AMP.

PATENTED mm 3 1 3.828.829

SHEET 3 OF 3 FLUID WEFT KNSERTHNG ARRANGEMENT 01F FLUID-JET LOOM The present invention relates generally to looms and particularly to fluid-jet shuttleless looms. More specifically, the invention is concerned with a weft inserting arrangement of the fluid-jet shuttleless loom.

The fluid-jet loom is adapted to feet weft yarns into the shed of warp yarns by the aid of a fluid jet which emerges in predetermined cycles from atleast one nozzle. The fluid is pumped to the nozzle under the control of a cam which is driven in synchronism with weaving cycles of the loom. The timing and duration of the fluid being ejected from the nozzle or nozzles are therefore fixedly determined by a given configuration of the cam and operational variables of mechanical elements associated with the cam, necessitating meticulous and timeconsuming adjustments of the angular position of the cam and the operational variables of the associated elements. Neglecting such adjustment efforts would result in uneven weave of the resultant cloth and, for this reason, it has been desired to make available an arrangement which will permit ready and precise adjustments of the timing and duration of the shots of the fluid into the shed of the warp yarns prior to and even in the course of the weaving operation. Moreover, the use of the mechanical control means or the cam as above noted has resulted in retarded response of the weft inserting mechanism to the operating cycles of the loom, providing a causefor degraded quality of the cloth produced.

It is, thus, a principal object of the present invention to provide an improved weft inserting arrangement for the fluid-jet shuttleless loom wherein the drawbacks inherent in the prior art counterparts are advantageously eliminated.

It is another object of the invention to provide an improved weft inserting arrangement of the fluid-jet loom for permitting easy and precise adjustments, in a stepless fashion, of the timing and duration of the fluid-jet delivery prior to and even during the weaving operation.

It is still another object of the invention toprovide an improved weft inserting arrangement of the fluid-jet loom, the weft inserting arrangement being electrically controlled in synchronism with operating cycles of the loom so that the cycles are faithfully responded to by the weft inserting arrangement even whilst the loom is driven at an increased speed.

The weft inserting arrangement to accomplish these objects comprises a solenoid-operated valve interposed between the fluid jet nozzle and pumping means for passing and interrupting the flow of fluid pumped from the pumping means when opened and closed, electrical signal generating means for producing a pulse train which is substantially in synchronism with operating cycles of the loom, and a pulse modifier circuit responsive to the pulse train from the signal generating means for producing pulses in cycles synchronized with pulses of the above mentioned pulse train and having pulse widths which are variable at will, the pulse modifier circuit being connected to the solenoid-operated valve so that the valve is opened and closed in the cycles synchronized with the pulses from the circuit and having durations related to the widths of the pulses from the circuit. The pulse modifier circuit may preferably be a monostable multivibrator including a variable resistor to be predominant over the widths of the pulses delivered from the multivibrator.

The pressure of the fluid before emerging from the nozzle has been usually assumed to be substantially constant throughout the duration of each of the fluid jet delivery cycles. If this is the case, the leading end of the fluid jet spurting from the nozzle will decelerate approximately proportionally to distance as it departs from the nozzle. Experiments have revealed that the velocity of the weft yarn entrained by such a decelerating stream of fluid drops several per cent when the leading end of the fluid jet reaches an end of the shed of the warp yarns opposite to the nozzle. As a consequence, the stream of fluid advances more rapidly through the shed of the warp yarns close to the nozzle than through the shed remote from the nozzle. This results in slackening of the weft yarns that will cause irregular tensions of the weft yarns forming the resultant cloth and in formation of looped weft yarns that will critically deteriorate the quality of the cloth. It is, for these reasons, desired that the fluid is ejected from the nozzle by a decreasing pressure in every weft inserting cycle so that the jet of the fluid spurts from the nozzle at a lower velocity at a final stage of the weft inserting cycle.

Whereas, we have discovered as a result of various experiments that the long accepted hypothesis of the fluid pressure being maintained constant throughout the single weft inserting cycle and that the pressure of the fluid before emerging from the nozzle appreciably changes in each of the fluid jet delivery cycles. According to the results of the experiments we have conducted the pressure of the fluid before emerging from the nozzle rises steeply when the fluid flow control valve is opened and declines in an incipient stage of the valve being open. The pressure of the fluid behind the nozzle then rises appreciably until the flow control valve closes to shut off the flow of the fluid to the nozzle. The pressure of the fluid is higher in a later stage of the fluid jet delivery than inan earlier stage of the same. The reason accounting for this particular tendency has not yet been ascertained in the experiments we conducted, however a presumption may be made that the head of the fluid clue to the pressure is converted incipiently into a head due to the velocity of the fluid with a resultant decrease in the fluid pressure whereupon the velocity head of the fluid being passed to the nozzle acts to raise the pressure of the fluid ejected from the nozzle during the later stage of the fluid jet delivery cycle. In any event, the tendency of the fluid pressure increasing in the final stage of the fluid jet delivery cycle is objectional because such will aggrevate a problem in which the stream of fluid slows down as it approaches the end of the shed of the warp yarns remote from the fluid injection nozzle.

It is, therefore, still another principal object of the present invention to provide an improved solenoidoperated weft inserting arrangement of the fluid-jet shuttlesless loom wherein the weft yarns projected into the shed of the warp yarns are prevented from becoming slack or forming loops.

It is still another object of the invention to provide an improved solenoid-operated weft inserting arrangement of the fluid-jet loom, the weft inserting arrangement being adapted to shoot the weft yarn by a decreasing pressure during each of the weft inserting cycles.

Yet, it is another object of the invention to provide an improved solenoid-operated weft inserting arrangement of the fluid-jet loom wherein the weft inserting mechanism is adapted to project the weft yarn by a fluid pressure which decreases substantially linearly during every weft inserting cycle.

To accomplish these particular objects, the solenoidoperated weft inserting arrangement according to the present invention may further comprise accumulating means located intermediate between the pumping means and the solenoid-operated valve so that the fluid is passed at least partly from the accumulating means to the nozzle when the solenoid-operated valve is open.

Other objects and features of the solenoid-operated weft inserting arrangement according to the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view owing an overall construction of a representative example of the prior art fluidjet shuttleless loom;

FIG. 2 is a block diagram illustrating a preferred example of the weft inserting arrangement according to the present invention;

FIG. 3 is a graphical view showing waveforms of pulse trains produced in an electrical control circuit forming part of the weft inserting arrangement shown in FIG. 2;

FIG. 4 is a view which illustrates a preferred example of a pulse modifier circuit forming a part of the control circuit of the arrangement shown in FIG. 2;

FIG. 5 is a graphical view showing variations in the pressure of the fluid before emerging from the nozzle in the weft inserting arrangement illustrated in FIG. 2;

FIG. 6 is a schematic view showing another preferred embodiment of the weft inserting arrangement according to the present invention; and

FIG. 7 is a graphical view similar to FIG. 5 but now shows variations in the pressure of the fluid before emerging from the nozzle in the weft inserting arrangement which is illustrated in FIG. 6.

For the better understanding of the outstanding advantages of the fluid-jet weft inserting arrangement according to the present invention, description in some more detail will now be given of the water-jet loom using the conventional cam-operated wet inserting mechanism. In the prior art water-jet loom as seen in FIG. 1, the warp yarns 10 are continuously supplied in sheet form from a yarn beam over a back rest roller 12 and are shed as at 14 by means of healds 16. The warp yarns 10 thus forming the shed 14 are held parallelly spaced by a reed 18 and are ready to receive in the shed a weft yarn 20. The weft yarn 20 is injected into the shed 14 by means of a water-jet assisted weft inserting mechanism including a nozzle 22 directed across the shed 14 and a water feed pipeline 24 leading through a pumping unit 26 from a source (not shown) of water and terminating in the nozzle 22. The pumping unit 26 is cyclically driven from the drive means of the loom through engagement of a cam 28 and a spring-loaded cam follower 30. The cam 28 and cam follower 30 are so arranged that the pumping unit 26 delivers its output in synchronism with the timing of the warp yarns 10 being shed at 14. The weft yarn 20 is fed from a suitable thread package (not shown) in a predetermined length in every weft inserting cycle synchronized with the delivery cycle of the pumping unit 26 and is passed on to the nozzle 22. As the jet stream of water is ejected from the nozzle 22, the weft yarn 20 is entrained by the water jet and injected into the shed 14 of the warp yarns 10 throughout the width of the shed.

As will be apparent from the above description, the duration and timing of the delivery of the pumping init 26 are fixedly dictated by a given configuration of the cam 28 and a given spring constant responsible for the motion of the cam follower 30 throughout the weaving operation. It therefore follows that meticulous and time-consuming adjustments of the angular position of the cam 28 relative to the cam follower 30 and the amount of preload on the cam follower are required for the purpose of achieving proper timings in the weft inserting operations and for the selection of the delivery cycles of the pumping unit 26.

As previously mentioned, the drawback of the prior art fluid-jet loom of this nature can be eliminated by the use of the weft inserting arrangement according to the present invention in which the stream of fluid is shot from the nozzle the timing of which is regulated by a solenoid-operated valve responsive to the weaving cycles of the loom. A preferred embodiment of such a weft inserting arrangement will now be described with reference to FIG. 2.

Referring to FIG. 2, the weft inserting arrangement according to the present invention includes a main fluid feed pipe line 32 leading through a pumping unit 34 from a source (not shown) of fluid which is usually water. The main fluid feed pipeline 32 is in constant communication with a branch pipeline 36 which terminates in a fluid jet nozzle 38. Upstream of the fluid jet nozzle 38 is located a solenoid-operated valve 40 having a coil 40a surrounding a magnetic core 40b. The construction of the solenoid-operated valve 40 is well known in the art and, as such, no detailed description thereof will be herein incorporated.

An electrical control circuit is provided so as to energize and de-energize the solenoid coil 40a in accordance with the weaving cycles of the loom or, for example, in synchronism with the rotation of a suitable rotary element 42 of the loom. The control circuit comprises pulse signal generating means 44 operative to produce pulse signals synchronized with the weaving cycles of the loom. The signal generating means 44 may be in the form of a switch connected at one end to a power source 46 and delivers the pulse signals in response to the rotation of the rotary element 42. An example of the pulse train delivered at an output terminal of the signal generating means 44 is illustrated in (a) of FIG. 3. The pulses thus issuing from the signal generating means 44 are fed upon amplification by a preamplifier 48 to a pulse modifier 50 which is adapted to produce an output having a waveform shown in (b) of FIG. 3. The pulse modifier 50 is connected to the coil 40a of the solenoid-operated valve 40 through a suitable driver such as a power amplifier 52 to operate the valve 40 in response to the pulses of the waveform supplied from the pulse modifier. The nozzle 38 thus shoots jet streams of fluid with the weft yarn entrained by the streams in synchronism with the weaving cycles of the loom or the number of rotations of the rotary element 42 of the loom during the weaving operation. The timing and duration of the shots of the fluid stream from the nozzle 38 can be varied through selection of the time constants of the elements building the pulse modifier 50.

' A preferred example of the pulse modifier 50 is illustrated in FIG. 4, wherein the pulse modifier is constructed in the form of a monostable multivibrator. The monostable multivibratior comprises positive and negative bus lines 54 and 56, respectively, and a pair of transistors 58 and 60 connected between the bus lines. The transistor 58 has a collector electrode connected to the positive bus line 54 through a resistor 62 and an emitter electrode connected directly to the negative bus line 56. Likewise, the transistor 60 has a collector electrode connected to the positive bus line 54 through a resistor 64 and an emitter electrode connected directly connected to the negative bus line 56. The base circuit 60a of the transistor 60 is connected to an input terminal 66 of the multivibrator through a capacitor 68 and a node 70 between the collector electrode of the transistor 58 and the resistor 62. T be input terminal 66 is connected to the pre-amplifier 48 (FIG. 2) through a diode 72 which has its anode terminal connected to the collector electrode of the transistor 58, the resistor 62 and the capacitor 68 as shown. A variable resistor 74 is connected at one end to the positive bus line 54 and at the other end to a node 76 between the capacitor 68 and the base circuit 60a of the transistor 60. The base circuit 58a of the transistor 58' is connected through a resistor 78 to a node 80-between the collector electrode of the transistor 60 and the resistor 64. A resistor 82 is connected at one end to the negative bus line 56 and at the other end to a node 84 between the base circuit 58a of the transistor 58 and the resistor 78. The collector electrode of the transistor 60 and the resistors 64 and 78 are connected through the node 80 to an output terminal 86 of the multivibrator, the output terminal being connected through the power amplifier 52 to the solenoid coil 40a of the solenoid-operated valve 40 (FIG. 2).

When a negative pulse is absent at the input terminal 66, a voltage is impressed on the base circuit 60a of the transistor 60 which is therefore conducting, maintaining the potential on the collector electrode of the transistor 60 at zero. No output voltage is consequently delivered from the output terminal 86. When, under this condition, a negative voltage is applied through the diode 72 and the capacitor 68 to the base circuit 60a of the transisitor 60, then the base voltage of the transistor 60 drops so that the transistor 60 is rendered nonconductive, thereby delivering an output voltage to the output terminal 86 of the multivibrator. A voltage is consequently impressed upon the base circuit 58a of the transistor 58 which accordingly is rendered conductive. This will create a differential between the potentials on opposite electrodes c and c of the capacitor 68 so that the capacitor 68 commences charging. When the potential of the electrode c" of the capacitor 68 remote from the input terminal 66 reaches apredetermined level, then the potential on the base circuit 60a of the transistor 60 exceeds a predetermined value with the result that the transistor 60 is rendered conductive so as to cause the output voltage to disappear from the output terminal 86 of the multivibrator. The cyclic and alternate conduction of the two transistors 58 and 60 thus result in production of the pulse train having the waveform illustrated in (b) of FIG. 3. The pulsewidth of this waveform will be readily varied through selection of the resistance which is available of the variable resistor 64.

It will now be appreciated that the timing of the delivery of fluid from the pumping unit 34 to the fluid jet nozzle 38 is dictated by the rise times of the pulse train shown in (a) of FIG. 3 while the duration of the pump delivery is dictated by the pulse width of the pulse train indicated at (b) in FIG. 3. The timing and duration of the weft inserting cycles can thus be adjusted easily and precisely in a stepless fashion depending upon the types and counts of the weft yarns to be used so that a satisfactorily even weave will be obtained in the resultant cloth. The use of the electrical control unit will, moreover, provide improved response of the weft inserting arrangement to the operational cycles of the loom even when the loom is driven at an increased speed.

As previously noted, the pressure of the fluid from the fluid jet nozzle of the weft inserting arrangement initially decreases and thereafter appreciably increases in each of the cycles in which the fluid is ejected from the fluid jet nozzle. FIG. 5 represents a curve A which indicates the pressure in the nozzle or, in other words, the initial velocity of the fluid ejected from the nozzle in response to electrical pulse which are formed from pulse signals of a pulse train B which is produced from the signal generating means 44 in the control circuit shown in FIG. 2. Whem, thus, a pulse appears on the output terminal of the signal generating means so that the solenoid-operated valve opens, then the pressure of the fluid at the fluid jet nozzle rises suddently from zero level to A on curve A. The fluid pressure then decreases for a short while and thereafter rises until the pulse from th control circuit (which in this instance may be the monostable multivibrator issuing the pulse train indicated in (b) of FIG. 3) disappears. When the pulse from the control circuit thus disappears, the fluid pressure drops suddenly as indicated at A on curve A in FIG. 5 so that the particular weft inserting cycle terminates. As will be evident from curve A in FIG. 5, the pressure of the fluid is lower than the level A during an early fluid jet delivery stage t and higher than the level A during a later fluid jet delivery stage t in each of the weft inserting cycles. It will be further seen in FIG. 5 that the fluid pressure in the nozzle developed at t e later stage t; is appreciably higher than the fluid pressure which is built up at the early stage 1 This and the' fact that the velocity of the stream of fluid after emerging from the fluid jet nozzle declines as it advan'ces from the nozzle are objectionable from the view point of preventing the weft yarns from becoming slack or forming loops in the shed of the warp yarns. Thus, the present invention further provides solution to this problem, and, accordingly, a preferred embodiment of the weft inserting arrangement adapted for this purpose is illustrated in FIG. 6, wherein parts corresponding to those incorporated in the embodiment shown in FIG. 2 are designated by like reference numerals.

Referring to FIG. 6, the weft inserting arrangement invariably includes a main fluid feed pipeline 32 which is in constant communication with a source (not shown) of fluid such as water through a suitable pumping unit (not shown). The pipeline 32 is branched to a branch pipeline 36 which terminates in a fluid jet nozzle 38 through a solenoid-operated valve 40. The solenoid-operated valve 40 is controlled by an electrical control circuit which has been described with reference to FIG. 2 and further with reference to FIG. 4 so as to regulate the delivery of the fluid to the nozzle 36 in the described manner for projecting the weft yarn 20 from the nozzle 32 the timing and duration being synchronized with the operating cycles of the loom and thus predetermined.

An accumulator unit 88 is incorporated in the branch pipeline 36 anterior to the solenoid-operated valve 40 so that the fluid upstream of the valve is constantly subjected to a certain pressure. The accumulator unit 88 may be of any of the constructions commonly in use but the same may preferably be of the type including an expansible and compressible gas chamber which is defined by a flexible membrane and which is filled with gas under pressure. To prevent delay of the response of the fluid in the accumulator to the opening of the solenoid-operated valve 40 and to minimize the impetus of the fluid passing to the nozzle 38, it is preferred that the accumulator unit 88 be positioned as close to the nozzle 38 as possible. According to the results of the experiments conducted by us, it has turned cut that the accumulator should have a capacity which is several to several tens of times greater than the quantity of the fluid ejected from the nozzle 38 in one weft inserting cycle. If the accumulator unit 88 has an insufficient capacity, then the accumulator unit will lose its significance. If, on the contrary, the accumulator unit has an excessively large capacity the pressure of the fluid before being ejected from the nozzle at the initial and final stages of each fluid jet delivery cycle will be substantially equalized to each other so that the weft yarn projected into the shed of the warp yarns tends to be come slack or to form a loop by reason of the differential velocity of the stream of the fluid at the opposite ends of the shed. 1

Experiments were conducted by use to ascertain the effectiveness of the provision of the accumulator unit in the solenoid-operated weft inserting arrangement accroding to the present invention. The accumulator unit used in the experiments had a capacity of about 30 cm and was filled with gas pressurized to about 9 kgs/cm Water was fed to the branch pipeline at a pressure of 20 to 28 kgs/cm and was ejected from the fluid jet nozzle in a quantity of 3 cm in each of the weft inserting cycles. The quantity of the water stored in the accumulator was approximately 20 cm because the total capacity of the expansible and compressible chamber filled with pressurized gas was reduced to about onethird when subjected to water pressure. The variation of the pressure of the fluid before being ejected from the nozzle under these conditions is indicated by curve C in FIG. 7 wherein curve D demonstrates a waveform of the pulse train introduced into the electrical control circuit for the solenoid-operated valve similarly to the curve B of FIG. 5. When the pulse signals synchronized with the operating cycles of the loom are supplied as indicated by curve D, the solenoid-operated valve opens so that the pressure of the fluidbehind the fluid jet nozzle suddenly rises to a level indicated by C starting the weft inserting cycle. The fluid pressure then declines unit it reaches a level C at the end of the weft inserting cycle and suddenly drops to zero when the duration of the pulse applied to the solenoid-operated valve terminates. The experiments have revealed that the fluid pressure C at the final stage of the weft inserting cycle-is approximately 10 per cent lower than the fluid pressure C developed at the initial stage of the cycle. As a consequence, the initial velocity of the stream of fluid ejected from the nozzle decreases substantially in a linear fashion from the initial stage to the final stage of the weft inserting cycle with the result that the weft yarn is projected substantially at a constant velocity throughout the shed of the warp yarns. According to the results of the experiments, the velocity of the stream of fluid is approximately 5 per cent lower at the end of the shed remote from the nozzle than the velocity of the fluid stream initially ejected from the nozzle.

The solenoid-operated weft inserting arrangement having the accumulator unit as above described is thus useful for the purpose of achieving a substantially uniform tension in the weft yarn being projected into the shed of the warp yarns so that weft yarn can be prevented from becoming slack or forming a loop in the shed.

What is claimed is:

1. A weft yarn inserting arrangement in a fluid-jet loom, comprising a fluid jet nozzle directed across a shed of warp yarns, fluid pumping means communicating with said fluid jet nozzle for pumping fluid to the nozzle, a solenoid-operated valve positioned intermediate between said nozzle and said pumping means for providing intermittent fluid communication between the nozzle and pumping means when opened and closed, electrical signal generating means for producing a pulse train which is substantially in synchronism with operating cycles of said loom, and a pulse modifier circuit responsive to said pulse train from the signal generating means for producing pulses which are in synchronism with pulses of said pulse train and having pulse widths which are variable at will, said pulse modifier circuit being electrically connected to said solenoid-operated valve for opening and closing the valve in cycles which are substantially synchronized with the pulses supplied thereto from said pulse modifier circuit and having durations which are related to said pulse widths.

2. A weft yarn inserting arrangement as claimed in claim 1, further comprising fluid accumulating means located intermediate between said pumping means and said solenoid-operated valve for temporarily storing the fluid from said pumping means. a

3. A weft yarn inserting arrangement as claimed in claim 2, in which said fluid accumulating means has an expansible and compressible chamber which is filled with gas under pressure.

4. A weft yarn inserting arrangement as claimed in claim 1, in which said pulse modifier circuit comprises positive and negative bus lines, first and second transistors each having a collector electrode connected to the positive bus line through a resistor'and an emitter electrode connected to the negative bus line, an input terminal connected to the collector electrode of said first transistor and the resistor associated therewith, an output terminal connected to the collector electrode of said second transistor and the resistor associated therewith, a capacitor which is connected at one electrode to said input terminal and at the other electrode to the base circuit of said second transistor, resistors connected to a base circuit of said first transistor and respectively to said negative bus line and to said output terminal, and a variable resistor connected at one end to said positive bus line and at the other to said other electrode of said capacitor and to said base circuit of said second transistor. 

1. A weft yarn inserting arrangement in a fluid-jet loom, comprising a fluid jet nozzle directed across a shed of warp yarns, fluid pumping means communicating with said fluid jet nozzle for pumping fluid to the nozzle, a solenoid-operated valve positioned intermediate between said nozzle and said pumping means for providing intermittent fluid communication between the nozzle and pumping means when opened and closed, electrical signal generating means for producing a pulse train which is substantially in synchronism with operating cycles of said loom, and a pulse modifier circuit responsive to said pulse train from the signal generating means for producing pulses which are in synchronism with pulses of said pulse train and having pulse widths which are variable at will, said pulse modifier circuit being electrically connected to said solenoid-operated valve for opening and closing the valve in cycles which are substantially synchronized with the pulses supplied thereto from said pulse modifier circuit and haVing durations which are related to said pulse widths.
 2. A weft yarn inserting arrangement as claimed in claim 1, further comprising fluid accumulating means located intermediate between said pumping means and said solenoid-operated valve for temporarily storing the fluid from said pumping means.
 3. A weft yarn inserting arrangement as claimed in claim 2, in which said fluid accumulating means has an expansible and compressible chamber which is filled with gas under pressure.
 4. A weft yarn inserting arrangement as claimed in claim 1, in which said pulse modifier circuit comprises positive and negative bus lines, first and second transistors each having a collector electrode connected to the positive bus line through a resistor and an emitter electrode connected to the negative bus line, an input terminal connected to the collector electrode of said first transistor and the resistor associated therewith, an output terminal connected to the collector electrode of said second transistor and the resistor associated therewith, a capacitor which is connected at one electrode to said input terminal and at the other electrode to the base circuit of said second transistor, resistors connected to a base circuit of said first transistor and respectively to said negative bus line and to said output terminal, and a variable resistor connected at one end to said positive bus line and at the other to said other electrode of said capacitor and to said base circuit of said second transistor. 